現在完成時 和過去完成

　　定義現在完成時用來表示之前已發生或完成的動作或狀態，其結果的確和現在有聯系。動作或狀態發生在過去　但它的影響現在還存在;也可表示持續到現在的動作或狀態。其構成： have (has) +過去分詞。

　　用法：

　　1) 現在完成時所表示的動作在說話之前已完成，但對現在有影響，句中沒有具體的時間狀語。此時多于never， ever， just，before，already，yet等連用。

　　2) 現在完成時所表示的動作開始于過去，持續到現在，也許還會繼續持續下去。常與for，since等一段時間狀語連用。

　　注意：表示暫短動作的詞(如come，go，borrow，lend，die，bur，marry等)的完成時不能與for，since等表示一段時間的狀語連用。

　　例如：How long may I keep the book?這本書我可以借多久?

　　Two weeks

　　Borrow和lend 都是暫短性動詞，當表示借多久時，用動詞keep

　　常見的短暫性動詞轉換成延續性動詞

　　leave --- be away, borrow --- keep, buy --- have, begin/start --- be on, die --- be dead, finish --- be over, join --- be in+組織機構,

　　be a member of+組織機構, open sth --- keep sth open,

　　fall ill --- be ill, get up---be up, catch a cold --- have a cold,

　　come here --- be here, go there --- be there, become --- be,

　　come back --- be back, fall asleep --- be asleep,

　　get to/ arrive/reach --- be (in), leave --- be away from,

　　get to know --- know, go (get) out →be out，

　　put on→ wear;catch a cold →have a cold等。

　　例:The old man died 4 years ago. ----The old man has been dead for 4 years. ---- It is 4 years since the old man died. ----Four years has passed since the old man died.

　　He joined the Party 2 years ago. -----He has been in the Party for 2 years. I bought the book 5 days ago. ---- I have had the book for 5 days.

　　比較過去時與現在完成時

　　1)過去時表示過去某時發生的動作或單純敘述過去的事情，強調動作;現在完成時為過去發生的，強調過去的事情對現在的影響，強調的是影響。

　　2)過去時常與具體的時間狀語連用，而現在完成時通常與模糊的時間狀語連用，或無時間狀語。

　　一般過去時的時間狀語:

　　yesterday, last week，…ago, in1980, in October, just now, 具體的時間狀語

　　現在完成時的時間狀語

　　for, since, so far, ever, never, just, yet,　till / until, up to now, in past years, always,

　　3)現在完成時可表示持續到現在的動作或狀態，動詞一般是延續性的，如live, teach, learn, work, study, know.

　　過去時常用的非持續性動詞有come, go, leave, start, die, finish, become, get married等。

　　舉例：

　　I saw this film yesterday.(強調看的動作發生過了。)

　　I have seen this film. (強調對現在的影響，電影的內容已經知道了。)

　　句子中如有過去時的時間副詞(如 yesterday, last, week, in 1960)時，不能使用現在完成時，要用過去時。

　　(錯)Tom has written a letter to his parents last night.

　　(對)Tom wrote a letter to his parents last night.

　　句子中如有過去時的時間副詞(如 yesterday, last, week, in 1960)時，不能使用現在完成時，要用過去時。

　　(錯)Tom has written a letter to his parents last night.

　　(對)Tom wrote a letter to his parents last night.

　　用一般過去時代替完成時

　　1)　兩個動作如按順序發生，又不強調先后，或用then，and，but 等連詞時，多用一般過去時。

　　When she saw the mouse，she screamed.

　　My aunt gave me a hat and I lost it.

　　2 ) 兩個動作相繼發生，可用一般過去時;如第一個動作需要若干時間完成，用過去完成時。

　　When I heard the news, I was very excited.

　　3)　敘述歷史事實，可不用過去完成時，而只用一般過去時。

　　Our teacher told us that Columbus discovered America in 1492.

　　用于現在完成時的句型

　　1)It is the first / second time…. that…結構中的從句部分，用現在完成時。

　　It is the first time that I have visited the city.

　　It was the third time that the boy had been late.

　　2)This is the… that…結構，that 從句要用現在完成時.

　　This is the best film that I've (ever) seen.

　　這是我看過的最好的電影。

　　This is the first time (that) I've heard him sing.　這是我第一次聽他唱歌。

　　典型例題

　　(1) ---Do you know our town at all?

　　---No, this is the first time I ___ here.

　　A. was　 B. have been　 C. came　 D. am coming

　　答案B. This is the first time 后面所加從句應為現在完成時，故選B。

　　(2) ---Have you ____ been to our town before?

　　---No, it's the first time I ___ here.

　　A. even, come　 B. even, have come　　C. ever, come　 D. ever, have come

　　答案D. ever意為曾經或無論何時，反意詞為never，此兩詞常用于完成時。 This is the largest fish I have ever seen. It is / was the first time +that-clause 的句型中，從句要用完成時。

　　注意：非延續性動詞的否定形式可以與表示延續時間的狀語連用。即動作不發生的狀態是可以持續的。

　　(錯)I have received his letter for a month.

　　(對)I haven't received his letter for almost a month.

　　比較since和for

　　Since 用來說明動作起始時間，for用來說明動作延續時間長度。

　　I have lived here for more than twenty years.

　　I have lived here since I was born..

　　My aunt has worked in a clinic since 1949.

　　Some new oilfields have been opened up since 1976.

　　I have known Xiao Li since she was a little girl.

　　My brother has been in the Youth League for two years.

　　I have not heard from my uncle for a long time.

　　注意：并非有for 作為時間狀語的句子都用現在完成時。

　　I worked here for more than twenty years.

　　(我現在已不在這里工作。)

　　I have worked here for many years.

　　(現在我仍在這里工作。)

　　小竅門：　當現在完成時+一段時間，這一結構中，我們用下面的公式轉化，很容易就能排除非延續動詞在完成時中的誤使。

　　1)　(對) Tom has studied Russian for three years.

　　= Tom began to study Russian three years ago, and is still studying it now.

　　2)　(錯) Harry has got married for six years.

　　= Harry began to get married six years ago, and is still getting married now.

　　顯然，第二句不對，它應改為 Harry got married six years ago.　或 Harry has been married for six years.

　　since的四種用法

　　1) since +過去一個時間點　(如具體的年、月、日期、鐘點、1980, last month, half past six)。

　　I have been here since 1989.

　　2) since +一段時間+ ago

　　I have been here since five months ago.

　　3) since +從句　Great changes have taken place since you left.

　　4) It is +一段時間+ since從句

　　It is two years since I became a postgraduate student.

　　延續動詞與瞬間動詞

　　1) 用于完成時的區別

　　延續動詞表示經驗、經歷; 瞬間動詞表示行為的結 果，不能與表示段的時間狀語連用。

　　He has completed the work.　　他已完成了那項工作。 (表結果)

　　I've known him since then.　　 我從那時起就認識他了。(表經歷)

　　2)　用于till / until從句的差異

　　延續動詞用于肯定句，表示"做……直到……" 瞬間動詞用于否定句，表示"到……，才……"

　　He didn't come back until ten o'clock.

　　他到10 點才回來。

　　He slept until ten o'clock.

　　他一直睡到10點。

　　典型例題

　　1. You don't need to describe her. I ___ her several times.

　　A. had met　B. have met　 C. met　D. meet

　　答案B. 首先本題后句強調對現在的影響，我知道她的模樣，你不用描述。再次，several times告知為反復發生的動作，因此用現在完成時。

　　2.---I'm sorry to keep you waiting.

　　---Oh, not at all. I ___ here only a few minutes.

　　A. have been　 B. had been　 C. was　D. will be

　　答案A. 等待的動作由過去開始，持續到現在，應用現在完成時。

　　(四)過去完成時

　　1) 概念：表示過去的過去

　　其構成是had +過去分詞構成

　　2) 用法

　　a.　在told, said, knew, heard, thought等動詞后的賓語從句。

　　She said (that) she had never been to Paris.

　　b. 狀語從句

　　在過去不同時間發生的兩個動作中，發生在先，用過去完成時;發生在后，用一般過去時。

　　When the police arrived, the thieves had run away.

　　3)　過去完成時的時間狀語before, by, until , when, after, once, as soon as。

　　He said that he had learned some English before.

　　By the time he was twelve, Edison had began to make a living by himself.

　　Tom was disappointed that most of the guests had left when he arrived at the party.

　　典型例題

　　The students ___ busily when Miss Brown went to get a book she ___ in the office.

　　A. had written, left　B，were writing, has left　 C. had written, had left　D. were writing, had left

　　答案D. "把書忘在辦公室"發生在"去取書"這一過去的動作之前，因此"忘了書"這一動作發生在過去的過去，用過去完成時。句中when表示的是時間的一點，表示在"同學們正忙于……"這一背景下，when所引導的動作發生。因此

　　注意：　had no … when　　　　　還沒等…… 就……

　　had no sooner… than　　剛…… 就……

　　He had no sooner bought the car than he sold it.

　　過去完成時與現在完成時的比較

　　I have known him for three years.我認識他三年了。

　　I had known him when I was a student.

　　我當學生時，就已經認識他了。

　　過去完成時與現在完成時二者用法基本相同，但現在完成時以現在的時間為基點，過去完成時則以過去的時間為基點，與現在無關，即過去的過去。

　　I have finished my experiment.

　　我已經做完實驗了。

　　(表示現在說話時已經做完實驗)

　　By six o'clock，I had finished my experiment.

　　在六點以前，我就已經做完實驗了。

　　(表示在過去的某一時間six o'clock以前已經做完實驗，與現在毫無關系)

　　注意

　　過去完成時，主要用于間接引語中。